error: array lengths can't depend on generic parameters

[jonathanstrong]

ran into this error with nightly (via $ cargo check on master at 4ac62c2):

error: array lengths can't depend on generic parameters
   --> src/sgemm_kernel.rs:223:40
    |
223 |     let mut ab = [_mm256_setzero_ps(); MR];
    |                                        ^^

$ rustc --version
rustc 1.42.0-nightly (a9dd56ff9 2019-12-30)

haven't been able to make much headway in understanding what changed in rustc, but it seems likely this is a compiler bug.

It looks like substituting a const fn implemented on the struct does work (current implementation seems to rely on trait associated constants).

update: for a quick workaround, roll-back to nightly-2019-12-25 (ho ho ho!)

[azriel91]

Related issue: rust-lang/rust#67743

[norru]

Reproduced in:

• (nightly) rustc 1.42.0-nightly (859764425 2020-01-07)

Works in:

• (stable) rustc 1.40.0 (73528e339 2019-12-16)

[bluss]

Thanks! As you know, this code compiles since Rust 1.28, so it's unfortunate that it is broken on nightly.

[vladbat00]

I was able to compile it on rustc 1.42.0-nightly (6d3f4e0aa 2020-01-25), Windows 10

[bluss]

The issue has been fixed in Rust and is fixed in Rust 1.42. It will continue to be an issue (unless further changes are done in matrixmultiply) with older versions, but it is probably too late to matter now.